This invention relates to a magnetic disk to be mounted in a magnetic disk device such as a hard disk drive (HDD) and a manufacturing method of the magnetic disk.
A magnetic disk is a magnetic recording medium to be mounted in a magnetic disk device such as a hard disk drive (HDD). A hard disk drive has at least a magnetic disk and a magnetic head. With this structure, information is recorded on and reproduced from the magnetic disk by the magnetic head.
The magnetic disk is formed by stacking layers such as an underlayer, a magnetic layer, a protection layer, and a lubrication layer in this order on a substrate.
The underlayer is a layer formed for controlling grains of the magnetic layer and has a function of controlling an easy magnetization direction of the magnetic layer to be oriented in an in-plane direction of the disk or in a normal direction of the disk.
The underlayer also has a function of controlling the grain size of the magnetic layer.
The underlayer serves to miniaturize grains of the magnetic layer and, for example, exhibits a function of improving the signal-to-noise intensity ratio (S/N) of the magnetic recording medium or a function of improving the static magnetic properties thereof.
A technique with respect to an underlayer is disclosed, for example, in United States Letters Patent, U.S. Pat. No. 5,800,931 Publication. This U.S. Pat. No. 5,800,931 Publication describes that it is preferable to use an underlayer having a B2 crystal structure such as NiAl or FeAl.
As another technique, there is known, for example, a technique described in United States Letters Patent, U.S. Pat. No. 5,789,056 Publication. This U.S. Pat. No. 5,789,056 Publication describes a technique to interpose a CrTi alloy layer between a substrate and an underlayer.
As still another technique, there is known a technique of Japanese Unexamined Patent Application Publication, Tokkai 2004-086936 Publication (Japanese patent application Laid Open Kokai No. 2004-086936). In this technique, it is disclosed to use an alloy underlayer having a Fe7W6 structure. This publication discloses that use can be made, as an alloy forming the Fe7W6 structure, of each of various alloys such as a Co—W based alloy, a Co—Mo based alloy, a Co—Ta based alloy, a Co—Nb based alloy, a Ni—Ta based alloy, Ni—Nb based alloy, a Fe—W based alloy, a Fe—Mo based alloy, and a Fe—Nb based alloy.
As still another technique, there is known a technique of Japanese Unexamined Patent Application Publication, Tokkai 2004-326844 Publication (Japanese patent application Laid Open Kokai No. 2004-326844). In this publication, it is disclosed to use a nonmagnetic amorphous layer. This publication discloses that use can be made, as the nonmagnetic amorphous layer, of each of various alloys such as NiP, NiPB, NiZr, NiZrB, NiCrMoC, FeB, FeP, FePC, FeZrB, FeCrMoPC, CoZr, CoZrB, TiCr, CrB, TaB, CrTa, NiTa, CoW, and CoTa.
As still another technique, there is known a technique of Japanese Unexamined Patent Application Publication, Tokkai 2004-152424 Publication (Japanese patent application Laid Open Kokai No. 2004-152424). This publication discloses that use can be made of a W—Ru based alloy layer, a W—Re based alloy layer, a Mo—Ru based alloy layer, or a Mo—Re based alloy layer.
In recent years, the storage information amount required to HDDs has significantly increased. Recently, the information recording density has been required to be 60 Gbits/inch2 or more. In order to satisfy such a requirement for higher recording density, various developments have been made, but it has become difficult to achieve a sufficient S/N ratio.
Further, it has been required to achieve a sufficient S/N ratio even when information is recorded/reproduced at a high recording density of 800 kfci or more as a linear recording density.